The petrochemical and refining industries generally process or treat a hydrocarbon material using various catalytic processes that are carried out in a reactor vessel. Typically, such processes involve reacting the hydrocarbon material with hydrogen in a series of catalyst beds, each of which is made up of a material that is suited for the type of hydroprocess performed in the particular bed. These processes are performed at high temperatures, which must be controlled to ensure that the process is carried out efficiently and with maximum yield, but without damaging the materials that make up the catalyst beds. Some degree of temperature control is generally achieved by mixing the hot hydrocarbon liquid feed stream with a cooler stream of hydrogen gas that is provided from an external source. This mixing occurs in quench zones that are provided above each catalyst bed. For instance, in many reactors, the mixing of the reactant streams in the quench zones is performed by a mixing device that is located above a distribution plate or tray in the quench zone that collects the mixed reactants and then distributes the mixture across the top of the underlying catalyst bed with the objective of achieving a uniform temperature distribution throughout the bed.
However, while the mixing and distribution of reactants may serve to generally control the temperature of the hydroprocess, a uniform temperature distribution throughout the bed often is not achieved. For instance, because the hydroprocess is exothermic, a temperature profile of the bed generally should indicate an increase in temperature from the top to the bottom of the bed. However, situations can arise where the temperature within a particular region or at a particular spot in the catalyst bed is higher or lower than expected. Such situations can occur due to inadequate mixing of the reactants so that the hotter hydrocarbon feed is not uniformly saturated with the cooler hydrogen gas or as a result of non-uniform distribution of the mixed reactants across the surface of the bed by the distribution tray, either of which may arise, for instance, due to obstruction of feed nozzles and/or distribution outlets. Additionally, hot spots or regions in the catalyst bed can result from uneven flow of the reactants through the catalyst bed due to regions in which the catalyst material is packed less densely than in other regions, the presence of impurities in the catalyst material, or regions in which the catalyst material has been damaged, such as due to coking. In other situations, the catalyst within certain regions may wear more quickly than in other regions, resulting in regions of lower reactivity and, consequently, temperatures that are lower than optimal. Any of these situations can produce undesirable results, since they can lead, for instance, to compromises in product yield, inefficient utilization of catalyst material, premature replacement of the catalyst bed, and/or dangerous “runaway” or upset conditions.